Generally, gland packings are used in the gland portion of a regulating valve to prevent the leakage of a fluid from the inside of a valve box of the regulating valve. For example, in the gland portion of a general regulating valve, a plurality of gland packings is laminated in the axial line direction of the valve stem via a spacer in the gap between the inner wall of a stuffing box provided above a valve box and a valve stem, and the gland packings are tightened by a packing flange via a packing follower. This structure applies a pressure (referred to below as a contact surface pressure) to the contact surface between the gland packings and the surface of the valve stem and to the contact surface between the gland packings and the inner wall of the stuffing box, and this pressure prevents the leakage of the fluid in the valve box from the gap between the valve stem and the stuffing box.
In the regulating valve described above, since the gland packings expand when the temperature rises, the contact surface pressure between the gland packings and the valve stem rises. When the valve stem slides repeatedly in the state in which the contact surface pressure rises, the gland packings wear and the seal performance may degrade.
Accordingly, many regulating valves use disc springs to suppress increase in the contact surface pressure due to thermal expansion (see PTL 1). Specifically, as disclosed in PTL 1, a plurality of disc springs are laminated in the slide direction of the valve stem between the packing follower and the packing flange. Since this can release the increase in the volume of the gland packings due to thermal expansion as the displacement of the disc springs in the axial line direction of the valve stem via the packing follower, increase in the contact surface pressure between the gland packings and the valve stem can be suppressed.
However, as described in PTL 1, the conventional regulating valve uses a spring case to hold disc springs between the packing follower and the packing flange. Since this spring case has a relatively large size and high component cost among components included in the regulating valve, the number of disc springs that can be laminated between the packing follower and packing flange is limited and the production cost of the regulating valve becomes high.
On the other hand, PTL 2 discloses a regulating valve having the structure in which a plurality of disc springs disposed between the packing follower and the packing flange is held by the packing flange and gland nuts without using a spring case.